The present invention relates to the field of digital video compression. More specifically, the present invention relates to a statistical multiplexing algorithm designed to improve video quality.
In prior art statistical multiplexing schemes with limited group bandwidth, the bit rate demand (i.e. the “need parameter”) may be high on a large number of video channels simultaneously. In such an instance, a video channel may not receive the bandwidth it requires to maintain video quality. As a result, the encoder for that video channel will be forced into a panic quantization mode to prevent a video buffering verifier (VBV) model from underflowing, resulting in blocky video. In the panic quantization mode, all discrete cosine transformation (DCT) coefficients may be discarded.
Commonly assigned U.S. patent application Ser. No. 09/806,390, filed on Mar. 29, 2001 discloses one scheme for avoiding panic quantization mode in certain circumstances. In particular, the encoding of an I-frame is delayed when the VBV model does not have enough capacity to support an intra-coded (I) frame. However, there is a limitation in such a scheme that the I-frames cannot be spaced an infinite distance apart. Therefore, in a practical implementation of the invention described in U.S. patent application Ser. No. 09/806,390, the encoder is forced to encode an I-frame irregardless of the status of the VBV when the distance from the previous I-frame exceeds a predefined upper bound. If the buffer model does not have sufficient room to hold a normal I-frame, the encoder will be forced into panic quanitzation mode to avoid VBV underflow.
It would be advantageous to eliminate any potential for encoding in a panic quantization mode. It would be advantageous to artificially increase the bandwidth need parameter when the encoder delays encoding of an I-frame due to a buffer constraint, thereby increasing the share of bandwidth in that encoding channel.
The methods and apparatus of the present invention provide the foregoing and other advantages.